Figure 4.

A superposition (a) of the reconstructions with C₄ symmetry and one-start helical symmetry in which one subunit in each has been aligned (a, black arrow) shows the similarity of structure for subunits and difference in subunit packing. The yellow surface has C₄ symmetry with an axial rise of 12.8 Å and a twist of 34.2° (Fig. 2d), while the cyan surface has a one-start helical symmetry with a twist of 99.6° and an axial rise of 3.5 Å. (Fig. 3c). The aligned subunit in the yellow structure is shown as mesh for clarity. A surface lattice (b,c) shows the arrangement of subunits on the surface of a cylinder, using the convention that the cylindrical surface has been cut open and we are looking at the outside of the surface. Within segments having C₄ symmetry (b), the strongest observed connectivity between subunits is along the left-handed eight-start helices (red) and the right-handed four-start helices (cyan). Two helical families are labeled in the helical net for the one-start helix (c). The strongest observed connectivity between subunits within segments having a one-start symmetry is along the right-handed four-start helices (cyan) and the left-handed seven-start helices (red). A unit cell has been colored yellow (b,c) in each, showing that despite the differences in symmetry, the local packing is very similar between the two states.